<head>
<title>Manual Page</title>
</head>
<body>
<pre>
<a href="pca_lookup_file.html"><b>pca_lookup_file</b></a>                  <a href="pca_lookup_file.html"><b>pca_lookup_file</b></a>



</pre><h2>NAME</h2><pre>
       pca_lookup_file,    del_PathCache,    del_PcaPathConf,   new_PathCache,
       new_PcaPathConf, pca_last_error,  pca_path_completions,  pca_scan_path,
       pca_set_check_fn,  ppc_file_start,  ppc_literal_escapes - lookup a file
       in a list of directories

</pre><h2>SYNOPSIS</h2><pre>
       #include &lt;libtecla.h&gt;

       PathCache *new_PathCache(void);

       PathCache *del_PathCache(PathCache *pc);

       int pca_scan_path(PathCache *pc, const char *path);

       void pca_set_check_fn(PathCache *pc, CplCheckFn *check_fn,
                             void *data);

       char *pca_lookup_file(PathCache *pc, const char *name,
                             int name_len, int literal);

       const char *pca_last_error(PathCache *pc);

       CPL_MATCH_FN(pca_path_completions);



</pre><h2>DESCRIPTION</h2><pre>
       The PathCache object is part of  the  tecla  library  (see  the  libte-
       cla(@LIBR_MANEXT@) man page).

       PathCache objects allow an application to search for files in any colon
       separated list of directories, such as the unix execution PATH environ-
       ment  variable. Files in absolute directories are cached in a PathCache
       object, whereas relative directories are scanned  as  needed.  Using  a
       PathCache  object,  you can look up the full pathname of a simple file-
       name, or you can obtain a list of the possible completions of  a  given
       filename  prefix.  By  default all files in the list of directories are
       targets for lookup and completion, but a versatile  mechanism  is  pro-
       vided  for only selecting specific types of files. The obvious applica-
       tion of this facility is to provide Tab-completion and lookup  of  exe-
       cutable  commands  in  the  unix  PATH,  so  an optional callback which
       rejects all but executable files, is provided.


</pre><h2>AN EXAMPLE</h2><pre>
       Under UNIX, the following example program looks  up  and  displays  the
       full pathnames of each of the command names on the command line.

         #include &lt;stdio.h&gt;
         #include &lt;stdlib.h&gt;
         #include &lt;libtecla.h&gt;

         int main(int argc, char *argv[])
         {
           int i;
         /*
          * Create a cache for executable files.
          */
           PathCache *pc = new_PathCache();
           if(!pc)
             exit(1);
         /*
          * Scan the user's PATH for executables.
          */
           if(pca_scan_path(pc, getenv("PATH"))) {
             fprintf(stderr, "%s\n", pca_last_error(pc));
             exit(1);
           }
         /*
          * Arrange to only report executable files.
          */
          pca_set_check_fn(pc, cpl_check_exe, NULL);
         /*
          * Lookup and display the full pathname of each of the
          * commands listed on the command line.
          */
           for(i=1; i&lt;argc; i++) {
             char *cmd = pca_lookup_file(pc, argv[i], -1, 0);
             printf("The full pathname of '%s' is %s\n", argv[i],
                    cmd ? cmd : "unknown");
           }
           pc = del_PathCache(pc);  /* Clean up */
           return 0;
         }

       The following is an example of what this does on my laptop under linux:

         $ ./example less more blob
         The full pathname of 'less' is /usr/bin/less
         The full pathname of 'more' is /bin/more
         The full pathname of 'blob' is unknown
         $


</pre><h2>FUNCTION DESCRIPTIONS</h2><pre>
       In order to use the facilities of this module, you must first  allocate
       a PathCache object by calling the new_PathCache() constructor function.

         PathCache *new_PathCache(void)

       This function creates the resources needed to cache and lookup files in
       a list of directories. It returns NULL on error.


</pre><h2>POPULATING THE CACHE</h2><pre>
       Once you have created a cache, it needs to be populated with files.  To
       do this, call the pca_scan_path() function.

         int pca_scan_path(PathCache *pc, const char *path);

       Whenever this function is called, it discards the current  contents  of
       the  cache,  then  scans  the list of directories specified in its path
       argument for files. The path argument must be  a  string  containing  a
       colon-separated       list       of      directories,      such      as
       "/usr/bin:/home/mcs/bin:.". This can include directories  specified  by
       absolute pathnames such as "/usr/bin", as well as sub-directories spec-
       ified by relative pathnames such as "." or "bin". Files in the absolute
       directories  are  immediately cached in the specified PathCache object,
       whereas sub-directories, whose identities obviously change whenever the
       current  working  directory is changed, are marked to be scanned on the
       fly whenever a file is looked up.

       On success this function return  0.  On  error  it  returns  1,  and  a
       description of the error can be obtained by calling pca_last_error(pc).


</pre><h2>LOOKING UP FILES</h2><pre>
       Once the cache has been populated with files, you can look up the  full
       pathname   of   a   file,   simply   by   specifying  its  filename  to
       pca_lookup_file().

         char *pca_lookup_file(PathCache *pc, const char *name,
                               int name_len, int literal);

       To make it possible to pass this function a filename which is  actually
       part  of  a longer string, the name_len argument can be used to specify
       the length of the filename at the start of the name[] argument. If  you
       pass  -1  for  this length, the length of the string will be determined
       with strlen(). If the name[]  string  might  contain  backslashes  that
       escape  the  special  meanings  of spaces and tabs within the filename,
       give the literal argument,  the  value  0.  Otherwise,  if  backslashes
       should  be  treated  as  normal characters, pass 1 for the value of the
       literal argument.


</pre><h2>FILENAME COMPLETION</h2><pre>
       Looking up the potential completions of a filename-prefix in the  file-
       name  cache, is achieved by passing the provided pca_path_completions()
       callback function to the cpl_complete_word() function (see the cpl_com-
       plete_word(@FUNC_MANEXT@) man page).

         CPL_MATCH_FN(pca_path_completions);

       This  callback  requires that its data argument be a pointer to a PcaP-
       athConf object. Configuration objects of this  type  are  allocated  by
       calling new_PcaPathConf().

         PcaPathConf *new_PcaPathConf(PathCache *pc);

       This  function returns an object initialized with default configuration
       parameters, which determine  how  the  cpl_path_completions()  callback
       function  behaves. The functions which allow you to individually change
       these parameters are discussed below.

       By default, the pca_path_completions() callback function searches back-
       wards  for  the  start of the filename being completed, looking for the
       first un-escaped space or the start of the input line. If you  wish  to
       specify  a  different location, call ppc_file_start() with the index at
       which the filename starts in the input line. Passing start_index=-1 re-
       enables the default behavior.

         void ppc_file_start(PcaPathConf *ppc, int start_index);

       By  default,  when  pca_path_completions()  looks  at a filename in the
       input line, each lone backslash in the input  line  is  interpreted  as
       being a special character which removes any special significance of the
       character which follows it, such as a space which should  be  taken  as
       part  of the filename rather than delimiting the start of the filename.
       These backslashes are thus ignored while looking for  completions,  and
       subsequently  added  before spaces, tabs and literal backslashes in the
       list of completions. To have unescaped backslashes  treated  as  normal
       characters,  call  ppc_literal_escapes()  with  a non-zero value in its
       literal argument.

         void ppc_literal_escapes(PcaPathConf *ppc, int literal);

       When you have finished with a PcaPathConf variable, you can pass it  to
       the del_PcaPathConf() destructor function to reclaim its memory.

         PcaPathConf *del_PcaPathConf(PcaPathConf *ppc);



</pre><h2>BEING SELECTIVE</h2><pre>
       If  you  are  only  interested  in certain types or files, such as, for
       example, executable files, or files whose names  end  in  a  particular
       suffix, you can arrange for the file completion and lookup functions to
       be selective in the filenames that they return.  This is done by regis-
       tering  a  callback  function  with  your PathCache object. Thereafter,
       whenever a filename is found which  either  matches  a  filename  being
       looked  up, or matches a prefix which is being completed, your callback
       function will be called with the full pathname of the  file,  plus  any
       application-specific data that you provide, and if the callback returns
       1 the filename will be reported as a match, and if  it  returns  0,  it
       will  be  ignored.   Suitable  callback  functions and their prototypes
       should be declared with the following macro. The CplCheckFn typedef  is
       also provided in case you wish to declare pointers to such functions.

         #define CPL_CHECK_FN(fn) int (fn)(void *data, \
                                           const char *pathname)
         typedef CPL_CHECK_FN(CplCheckFn);

       Registering    one    of   these   functions   involves   calling   the
       pca_set_check_fn() function. In  addition  to  the  callback  function,
       passed  via  the  check_fn argument, you can pass a pointer to anything
       via the data argument. This pointer will be passed on to your  callback
       function,  via  its  own  data argument, whenever it is called, so this
       provides a way to pass appplication specific data to your callback.

         void pca_set_check_fn(PathCache *pc, CplCheckFn *check_fn,
                               void *data);

       Note that these callbacks are passed the full pathname of each matching
       file,  so the decision about whether a file is of interest can be based
       on any property of the file, not just its filename. As an example,  the
       provided cpl_check_exe() callback function looks at the executable per-
       missions of the file and the permissions of its parent directories, and
       only  returns  1  if  the user has execute permission to the file. This
       callback function can thus be used to lookup or complete command  names
       found  in  the  directories listed in the user's PATH environment vari-
       able. The example program given earlier in this  man  page  provides  a
       demonstration of this.

       Beware  that  if somebody tries to complete an empty string, your call-
       back will get called once for every file in the cache, which could num-
       ber  in  the  thousands. If your callback does anything time consuming,
       this could result in an unacceptable delay for the user,  so  callbacks
       should be kept short.

       To  improve performance, whenever one of these callbacks is called, the
       choice that it makes is cached, and the  next  time  the  corresponding
       file  is  looked  up, instead of calling the callback again, the cached
       record of whether it was accepted or rejected is used. Thus if somebody
       tries  to  complete  an  empty  string, and hits tab a second time when
       nothing appears to happen, there will only be one long delay, since the
       second  pass  will operate entirely from the cached dispositions of the
       files. These cached dipositions are discarded whenever  pca_scan_path()
       is called, and whenever pca_set_check_fn() is called with changed call-
       back function or data arguments.


</pre><h2>ERROR HANDLING</h2><pre>
       If pca_scan_path() reports that an error occurred by returning  1,  you
       can   obtain   a   terse   description   of   the   error   by  calling
       pca_last_error(pc). This returns an internal string containing an error
       message.

         const char *pca_last_error(PathCache *pc);



</pre><h2>CLEANING UP</h2><pre>
       Once  you  have  finished using a PathCache object, you can reclaim its
       resources by passing it to  the  del_PathCache()  destructor  function.
       This  takes a pointer to one of these objects, and always returns NULL.

         PathCache *del_PathCache(PathCache *pc);


</pre><h2>THREAD SAFETY</h2><pre>
       In multi-threaded programs, you should use the libtecla_r.a version  of
       the library. This uses POSIX reentrant functions where available (hence
       the _r suffix), and disables features that rely on non-reentrant system
       functions.  In  the  case  of this module, the only disabled feature is
       username completion  in  ~username/  expressions,  in  cpl_path_comple-
       tions().

       Using  the  libtecla_r.a  version of the library, it is safe to use the
       facilities of this module  in  multiple  threads,  provided  that  each
       thread uses a separately allocated PathCache object. In other words, if
       two threads want to do path searching, they should each call  new_Path-
       Cache() to allocate their own caches.


</pre><h2>FILES</h2><pre>
       libtecla.a    -    The tecla library
       libtecla.h    -    The tecla header file.


</pre><h2>SEE ALSO</h2><pre>
       <a href="libtecla.html"><b>libtecla</b></a>, <a href="gl_get_line.html"><b>gl_get_line</b></a>, <a href="ef_expand_file.html"><b>ef_expand_file</b></a>,
       <a href="cpl_complete_word.html"><b>cpl_complete_word</b></a>


</pre><h2>AUTHOR</h2><pre>
       Martin Shepherd  (mcs@astro.caltech.edu)



                                                <a href="pca_lookup_file.html"><b>pca_lookup_file</b></a>
</pre>
</body>
